Vehicle low tire pressure signal system

ABSTRACT

A low-pressure alarm system for pneumatic tires including a sensing unit operatively connected to each tire pressure, a detection unit carried by each stationary tire hub for detecting when the sensing unit is activated and a light panel connected to the detecting unit through a solid-state control circuit to indicate which tire assembly has a low pressure. The detection units are manually set to a detecting position and, once tripped by the associated sensing unit, remains tripped until manually reset.

United States Patent Mitchell et al.

VEHICLE LOW TIRE PRESSURE SIGNAL SYSTEM Inventors: Phillip G. Mitchell,305 Highland Avenue, Opelika, Ala. 3680]; Fredrick S. Hagans, 8 SouthChurch Street, Sylacauga, Ala. 35150; James Noel Baker, 445 OpelikaRoad, Auburn, Ala. 36830; Glenn R. Mc- Clendon, Opelika Highway, DrawerH, Lafayette, Ala. 36862 Filed: Apr. 24, 1970 Appl. No.: 31,514

US. Cl ..340/58, ZOO/61.25 Int. Cl. ..360c 23/02 Field of Search..340/58; 200/6122, 61.23, 61.25,

ZOO/61.26

[ Feb. 29, 1972 [56] References Cited UNITED STATES PATENTS 2,710,3916/1955 Trinca ..340/ss 3,508,193 4/1970 Giovannelli et 31.... ..34o/ss2,199,032 4/1940 Stoddard ..200/6l .26 3,271,736 9/1966 Brown et al..340/52 F Primary Examiner--Alvin H. Waring Attorney-Newton, Hopkins &Ormsby [57] ABSTRACT A low-pressure alarm system for pneumatic tiresincluding a sensing unit operatively connected to each tire pressure, adetection unit carried by each stationary tire hub for detecting whenthe sensing unit is activated and a light panel connected tovthedetecting unit through a solid-state control circuit to indicate whichtire assembly has a low pressure. The detection units are manually setto a detecting position and, once tripped by the associated sensingunit, remains tripped until manually reset.

4 Claims, 6 Draw g MA PATENTEUFEBZS I972 3,646,514

SHEET 2 OF 4 ,FIG 2 VEHICLE LOW TIRE PRESSURE SIGNAL SYSTEM BACKGROUNDOF THE INVENTION Pneumatic tires on present day vehicles frequentlybecome punctured or deflated for various reasons resulting many times inserious injury. This is especially true in heavy trucks since, when onetire of a set carried by a single wheel loses pressure, there is nowarning and the extra load transferred to the remaining tire causes sameto sometimes heat up and blow out.

SUMMARY OF THE INVENTION These and other problems associated with priorart low- BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a partialperspective view of a wheel and tire as sembly showing the oneembodiment of the invention installed thereon;

FIG. 2 is a cross-sectional view taken substantially along line 2-2 inFIG. 1;

pressure alarm systems are overcome by the invention dis.

closed herein in that it is simple in construction and can be easilyinstalled on existing equipment without altering same. Further, means isprovided for indicating a malfunction within the alarm system itself andthe light indicating which wheel assembly has a tire with low pressurepulsates when illuminated.

Accordingly, it is one of the objects of the invention to provide a lowpressure alarm system which provides a visual indication of low pressurein a particular set of tires carried on a wheel assembly.

Another object of the invention is to provide a low-pressure alarmsystem having means for visually indicating a malfunction within thealarm system itself.

A still further object of the invention is to provide a lowpressurealarm system which can be installed without modification of existingvehicle structures.

An additional object of the invention is to provide a lowpressure alarmsystem simple in construction and easily maintained.

Another object of the invention is to provide a low-pressure alarmsystem which provides not only a visual indication of the set of tireshaving a low pressure therein but also a visual indication of which tireof the set which has a low pressure.

A still further object of the invention is to provide a lowpressurealarm system which has certain built in safety features to preventmalfunction of said system.

Another object of the invention is to provide a low-pressure alarmsystem which does not alter the dynamic balance of the set of tires andwheel assembly when installed.

The apparatus of the invention includes a sensing unit associated witheach tire of a set and mounted for rotation with the set of tires, and adetection unit carried by each nonrotating hub portion of each wheelassembly. Each detection assembly is associated with an appropriateindicator light through a solid state control circuit to indicatevisually in the cab of the vehicle which set of tires has a low-pressuretire. The sensing unit that is activated provides a visual indication ofwhich tire of the set is deflated when the vehicle stops.

Each detection unit is manually set for sensing when a tire is deflatedand, upon activation, remains activated until manually reset to providea continuous signal. The control circuit includes a flasher section tocause the illuminated bulbs to flash to draw the drivers attentionthereto. Also included, in the control circuit is a malfunction detectorsection which senses if an indicator bulb is burned out and a signal issent thereto to illuminate same.

These and other features, objects and advantages of the inventiondisclosed herein will become more apparent on consideration of thefollowing specification and accompanying drawings wherein likecharacters of reference designate corresponding parts throughout and inwhich:

FIG. 3 is a longitudinal cross-sectional view of one embodiment of thesensing unit of the invention;

FIG. 4 is an electrical schematic diagram of one embodiment of thecontrol circuit of the invention;

FIG. 5 is a side elevational view of a second embodiment of the sensingunit of the invention; and,

FIG. 6 is a longitudinal cross-sectional view of the sensing unit ofFIG. 5.

These figures and the following detailed description of the inventiondisclose specific embodiments thereof, however, it is to be understoodthat the inventive concept is not limited thereto since it may beembodied in other forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Referring to thedrawings, and more particularly to FIG. 1, it will be seen that theinvention includes a sensing unit S associated with each tire T of avehicle, a detection unit D associated with each wheel assembly W of thevehicle, a control circuit C appropriately carried by the vehicle andoperatively connected to each detection unit D, and an indicator orannunciator panel A usually carried in the drivers cab of the vehicleand operatively connected to the control circuit C. The sensing unit Sis mounted on the rotating rims of the assembly W and the detection unitis carried by the fixed hub of the assembly W so that the unit S willpass in the vicinity of the unit D once per revolution of the tires T.

Referring to FIG. 2, the wheel assembly W carries a dual set of tires Tand includes a fixed hub 10 carried by axle housing 11. The axle l2rotatably extends therethrough to mount a brake drum l4 and drivingspider l5 thereon for rotation therewith. An outside rim 16 is bolted tospider l5 and an inside rim 18 engages the positioning lugs 19 on spider15. An annular spacer 20 extends between rims l6 and 18 to maintain themin a spaced apart relationship when clamped within spider 15 inconventional manner.

A pair of mounting brackets 21 are bolted to diametrically oppositesides of spacer 20 and are appropriately formed to extend toward theinner rim 18. A mounting leg 22 is provided on each which lies injuxtaposition with the inside of rim l8.

Each mounting leg 22 carries a sensing unit S thereon. The sensing unitS includes a cylindrical housing 25 as best seen in FIG. 3 defining acavity 26 therein opening onto one end of housing 25. A reduced diameterpiston passage 29 extends from the terminal end of cavity 26 to theopposite end of housing 25 and an annular recess 29 around the exit endof passage 28 is also defined in housing 25 A threaded pressure inletport 30 extends radially outward from the juncture of cavity 26 andpassage 28 to permit cavity 26 to be in communication with the airpressure in tire T through fitting 31 threadedly received in port 30.Fitting 31 communicates with tire T through hose 32 and connector 34 onvalve stem 35 of tire T as seen in FIG. 2

Referring back to FIG. 3, a sensor piston 36 is slidably received incavity 26 in sealing engagement therewith. Piston 36 defines a pair ofspaced annular grooves 37 therearound to receive a pair of resilientO-rings 38 therein. The O-rings 38 provide the sliding sealingengagement between the piston 36 and housing 25. An indicator piston rod39 is threadedly received in that side of piston 36 facing passage 28and protrudes through passage 28. Rod 39 is appropriately dimensionedfor the trip end 40 thereof to be retracted toward the right end ofhousing 25 when piston 36 is bottomed to the left as seen in FIG. 3.

A positioning boss 41 extends from that side of piston 36 opposite rod39 and a compression coil spring 42 is received therearound and withincavity 26. A closure plate 44 is received in the open end of cavity 26behind spring 42 and is attached to housing 26 by fasteners 45. Theplate 44 prevents ejection of spring 42 as piston 36 is moved to theleft in FIG. 3 to compress same and a vent 46 is defined therethrough toprevent an air lock between piston 36 and plate 44. The length andcompressive strength of spring 42 is such that the air pressure fromtire T through port 30 will fully retract rod 39 and piston 36 if thepressure is within the proper range specified by the manufacturer. Ifthe air pressure drops however, the spring 42 will cause rod 39 andpiston 36 to extend to expose the trip end 40 thereof and trip thedetection unit D associated therewith.

Rod 39 is maintained centered in passage 28 by a bushing 50 attached tothat end of housing 25 onto which recess 29 opens. Bushing 50 includesan annular detent 51 which extends into recess 29 to position a pair ofsealing O-rings 52 in recess 29 with an annular spacer 54 betweenO-rings 52. The detent 51 is dimensioned to force O-rings 54 intosealing engagement with recess 29 and rod 39 to seal the pressurechamber portion 55 of cavity 26 in combination with the rings 38 aroundpiston 36.

Only one of the sensing units S is described in detail since theconstruction is the same for each and like numbers will be applied toeach.

The detection unit D as best seen in FIGS. 1 and 2 is mounted on fixedhub by an inverted L-shaped mount 55 bolted thereto. The unit D ispositioned on mount 55 so that its activating wand 56, when set foractivation, extends to a position in the vicinity of the inside edge ofinner rim 18 and into the path of the trip ends 40 of the rods 38 whenthe air pressure in tires T is sufficiently low to allow spring 42 toextend same.

The wand 56 is rotatably carried by casing 58 and is mechanicallyconnected to a toggle switch mechanism (not shown) having contacts 8-1(see FIG. 4) which are open when wand 56 is in its detecting positionset for activation (see solid line position in FIG. 1) and closed whenwand 56 is in its deflected activated position (see dashed line positionin FIG. 1). The toggle switch mechanism is such that wand 56 will remainin its detecting or activated positions until forcibly moved to theother position. Therefore, once wand 56 is set in its detectingposition, it will remain there until tripped by rod 39 striking same toits activated position. Once tripped, wand 56 will remain in itsactivated position with contacts S-l closed until reset manually throughreset lever 59.

Referring to FIG. 4, the control circuit C includes a plurality ofswitch contact S-1 through 86 connected in parallel through indicatorbulbs L-l through L-8 respectively from voltage source V to commonground G. Contacts S-1 through 8-6 correspond to each wheel assembly ofthe vehicle and are the switch contacts of the detection units D. BulbsL-l through L-6 are carried by annunciator panel A and represent eachindividual wheel assembly respectively. Appropriate indicia may beprovided on panel A to identify the wheel assembly associated with thecorresponding light bulb.

Bulbs L-l through L-6 are neon lamps having a certain thresholdactivating voltage. The bulbs L-l through L-6 are connected in parallelto a pulsating voltage source from flasher section F of circuit Cthrough diodes D-l through D-6 respectively, resistor 11-8 and diode D7.Flasher section F includes transistors Q and Q appropriately connectedto voltage source V through resistors and capacitors to give a squarewave pulsating voltage output. The voltage supplied to bulbs L-l throughL-8 is insufficient in itself to exceed the threshold voltage thereof,but, once any one of contacts S-1 through S-6 is closed, its associatedbulb will illuminate since its threshold voltage is exceeded uponclosure of the switch. The voltage from section F now serves to pulsatethe bulb to flash same.

The voltage output from section F is also connected to ground G througha malfunction detection section M. Section M is connected to source Sthrough malfunction indicator bulb L-7. Section M includes a transistorQ appropriately connected to section F and bulb L-7 so that transistor Qwill conduct if one of bulbs L-l through L-7 is blown to open thatportion of the circuit. This causes bulb 11-1 to be illuminated if anybulbs L-1 through L-6 malfunction. 1

The transistors Q1, Q2 and Q; are NPN transistors designated 2N3643. Thevalues of the resistors and capacitors of circuit C are set forth inTable I.

Referring to FIGS. 5 and 6, it will be seen that a second embodiment ofthe sensing unit is shown and designated S. The units S can be used inlieu of units S and are adapted to trip the wands 56 of detection unitsD in the same manner as the units S. The unit S will extend itsindicator rod 139 further than unit S for the same amount of travel ofits piston 136 as compared with that of piston 36 in unit S.

. The unit S includes a housing much larger in diameter than housing 25.Housing 125 defines a cavity 126 therein offset from the centerline ofhousing 125 and having a diameter substantially equal in dimensions tothat of cavity 26. A passage 128 similar to rod passage 28 extends fromone end of cavity 126 through housing 125 in alignment with thecenterline of cavity 126. A vent 146 extends from the opposite end ofcavity 126 to vent same to the atmosphere. The recess 129 is definedabout the exit end of passage 128.

A piston 136 is slidably received in cavity 126 in sealing engagementtherewith through O-rings 138 carried in grooves 137 around piston 136.A spring 142 similar to spring 42 is carried in cavity 126 betweenpiston 136 and the vent end of cavity 126 to force piston 136 to theleft toward passage 128 as seen in FIG. 5. A piston rod 160 is threadedinto piston 136 to slidably extend through passage 128 and a bushingthrough detent 151, O-rings 152 and spacer 154 in recess 129 maintainrod 160 centered in passage 128. The O-rings 152 seal passage 128 todefine a pressure chamber in communication with the air pressure intires T through fitting 131 in port 130 similar to the unit S.

The driving end 161 of rod is pivotally connected to a drive link 162.Drive link 162 is rotatably pinned to outstanding bracket 164, anddefines a driven slot 165 in one end thereof and a driving slot 166 inthe opposite end thereof. Driven slot 165 is connected to the drivingend 161 of rod 164) through pin 168 so that as rod 160 is extended orretracted, link 162 will be drivingly pivoted.

Driving slot 166 is connected to the inner end of indicator rod 139which is slidably received through a passage 169 in housing 125diametrically opposite cavity 126 by pin 170. Therefore, it will be seenthat, as rod 1611 is extended by spring 142 as the air pressure inchamber 155 drops below that specified for safe operation, the link 162will be pivoted counterclockwise as seen in FIG. 5 to extend the tripend 140 of indicator rod 139. Due to the position of unit S on bracket21, the end 140 will now trip wand 56 of detection unit D as it passesthereby. It will also be noted that due to the greater distance traveledby the slot 166, more of rod 139 will be extended for the same amount ofpiston movement when compared with unit S.

The exposed link 162 and bracket 164 are enclosed by a cup-shaped covermember 171. Cover 1711 is attached to housing 125 by welding or someother conventional means to hold same in position and the working cavity172 defined by member 171 is of a size to permit full operation of link162.

From the foregoing, the operation of the invention is initiated byconnecting circuit C to the voltage source V, here shown as 24 volts DC,and by properly manipulating levers 59 of units D to position wands 56in their upright detecting positions. When one of the tires T losespressure, its associated sensing unit S or S extends rod 39 or 139 totrip wand 56 of the associated detection unit D to illuminate the properbulb on annunciator panel A. The operator can then stop the vehicle andcheck the appropriate wheel assembly for the deflated tire. By lookingtoward the back side of the indicated wheel assembly, the operator cantell which sensing unit S or S is activated to determine which tire isdeflated. The trip end 40 or 140 of rod 39 or 139 may be color coded toindicate activation by exposure of the colored area.

The Y-shaped valve stem 35 of each tire T allows air to be added orremoved from the tire while the system is connected. Either of theO-rings 38 is sufficient to seal around piston 36 and so are O-rings 52.Therefore, if one of the O-rings 38 or 52 fails, the system will stillremain operative. The same also applies for O-rings 138 or 152.

Since the sensing units S or S are mounted on diametrically oppositesides of flange 20, the balance of the rotating parts of assembly W andtires T is maintained. For a single tired assembly W, and appropriateweight (not shown) may be used to balance the wheel assembly.

While specific embodiments of the invention have been disclosed hereinit is to be understood that full use of modifications, equivalents, andsubstitutions may be made without departing from the scope of theinvention.

We claim: I

1. An alarm system for indicating a low-pressure condition of a tireincluding; a pressure sensing unit communicating with the pressure inthe tire, said unit including a trip member responsive to said tirepressure for extension thereof when said tire pressure drops below apredetermined point and for retraction thereof when said pressure isabove said point; and a detection unit operatively associated with saidsensing unit, said detection unit including a switch and an activatingmember for selectively opening and closing said switch, said activatingmember selectively extendable into the path of said trip member whenextended but out of the path of said trip member when retracted, saidtrip member causing said activating member to close said switch whensaid trip member is extended and contacts said activating member; andcontrol means operatively connected to said switch, said control meansincluding first light means caused .to be illuminated when said switchis closed; and flashing means for supplying a pulsating voltage to saidfirst light means when illuminated to cause same to flash; said pressuresensing unit including a housing defining a pressure chamber therein incommunication with the air pressure of said tire; a piston slidablyreceived in said chamber in sealing relation therewith a rod attached tosaid piston and slidably extending from said housing; the air pressureof said tire urging the piston in a direction to retract said rod intothe housing; resilient means urging the piston in a direction to causethe rod to be extended from said housing; a lever pivotally supported onthe end of said housing and having a short arm connected to said rod anda longer arm connected to said trip member, said trip member extendingthrough a bore in said housing parallel with the piston rod, whereby themovement of said trip member will be substantially greater than that ofsaid rod.

2. An alarm system as in claim 1 wherein the activating member of saiddetection unit includes a wand adapted to be engaged by said trip memberwhen the tire pressure is below normal, said wand being so mounted thatwhen so engaged it will be moved to switch-closing position and willremain in such position until manually resetting said wand totrip-engagingsposition.

An alarm system as in claim 2, wherein said control means furtherincludes malfunction surveillance means operatively connected to saidfirst light means and responsive to a malfunction of said first lightmeans to visually indicate such malfunction.

4. An alarm system as in claim 3 wherein said malfunction surveillancemeans includes a second light means and a transistor operativelyconnected to said first light means and said second light means, saidtransistor being responsive to a malfunction of said first light meansto cause said second light means to be illuminated.

1. An alarm system for indicating a low-pressure condition of a tireincluding; a pressure sensing unit communicating with the pressure inthe tire, said unit including a trip member responsive to said tirepressure for extension thereof when said tire pressure drops below apredetermined point and for retraction thereof when said pressure isabove said point; and a detection unit operatively associated with saidsensing unit, said detection unit including a switch and an activatingmember for selectively opening and closing said switch, said activatingmember selectively extendable into the path of said trip member whenextended but out of the path of said trip member when retracted, saidtrip member causing said activating member to close said switch whensaid trip member is extended and contacts said activating member; andcontrol means operatively connected to said switch, said control meansincluding first light means caused to be illuminated when said switch isclosed; and flashing means for supplying a pulsating voltage to saidfirst light means when illuminated to cause same to flash; said pressuresensing unit including a housing defining a pressure chamber therein incommunication with the air pressure of said tire; a piston slidablyreceived in said chamber in sealing relation therewith a rod attached tosaid piston and slidably extending from said housing; the air pressureof said tire urging the piston in a direction to retract said rod intothe housing; resilient means urging the piston in a direction to causethe rod to be extended from said housing; a lever pivotally supported onthe end of said housing and having a short arm connected to said rod anda longer arm connected to said trip member, said trip member extendingthrough a bore in said housing parallel with the piston rod, whereby themovement of said trip member will be substantially greater than that ofsaid rod.
 2. An alarm system as in claim 1 wherein the activating memberof said detection unit includes a wand adapted to be engaged by saidtrip member when the tire pressure is below normal, said wand being somounted that when so engaged it will be moved to switch-closing positionand will remain in such position until manually resetting said wand totrip-engaging position.
 3. An alarm system as in claim 2, wherein saidcontrol means further includes malfunction surveillance meansoperatively connected to said first light means and responsive to amalfunction of said first light means to visually indicate suchmalfunction.
 4. An alarm system as in claim 3 wherein said malfunctionsurveillance means includes a second light means and a transistoroperatively connected to said first light means and said second lightmeans, said transistor being responsive to a malfunction of said firstlight means to cause said second light means to be illuminated.